the -c and -w (critical and warning ranges respectively) reflect ranges differently depending on if you want a critical to be low (under 10 for example) or high (over 90). In the former case, say the Signal Level of a microwave device you are monitoring is critical when under 10% and warning under 20% then the format of the -w and -c would be:

-w 25: -c 10:

If on the other hand you are looking at Signal to Noise ratio where warning is 50 dB and critical is 75 dB then the command would be:

-w :50 -c :75

If you have say a table where numbers translate to other things, again using a Microwave example: